Genetically engineered Pichia pastoris yeast for conversion of glucose to xylitol by a single-fermentation process.

Xylitol is industrially synthesized by chemical reduction of D-xylose, which is more expensive than glucose. Thus, there is a growing interest in the production of xylitol from a readily available and much cheaper substrate, such as glucose. The commonly used yeast Pichia pastoris strain GS115 was shown to produce D-arabitol from glucose, and the derivative strain GS225 was obtained to produce twice amount of D-arabitol than GS115 by adaptive evolution during repetitive growth in hyperosmotic medium. We cloned the D-xylulose-forming D-arabitol dehydrogenase (DalD) gene from Klebsiella pneumoniae and the xylitol dehydrogenase (XDH) gene from Gluconobacter oxydans. Recombinant P. pastoris GS225 strains with the DalD gene only or with both DalD and XDH genes could produce xylitol from glucose in a single-fermentation process. Three-liter jar fermentation results showed that recombinant P. pastoris cells with both DalD and XDH converted glucose to xylitol with the highest yield of 0.078 g xylitol/g glucose and productivity of 0.29 g xylitol/L h. This was the first report to convert xylitol from glucose by the pathway of glucose-D-arabitol-D-xylulose-xylitol in a single process. The recombinant yeast could be used as a yeast cell factory and has the potential to produce xylitol from glucose.